Conventionally, an ejector device for a refrigerant cycle is described in JP 11-37577A. In the ejector device, upstream and downstream throttle portions are provided in a nozzle body at an upstream side of a jet port of the nozzle body, and a fluid passage is expanded from the downstream throttle portion as a throat portion toward the jet port so that refrigerant is decompressed in the fluid passage and the pressure energy of the refrigerant is converted to the speed energy of the refrigerant. In order to improve nozzle efficiency by converting the pressure energy of the refrigerant to the speed energy thereof, an expanding angle of a passage wall surface of a downstream side portion in the nozzle body is made smaller than an expanding angle of a passage wall surface of an upstream side portion in the nozzle body, thereby restricting a flow separation of the refrigerant from the passage wall surface and a generation of a scroll flow.
However, in the ejector device described in JP 11-37577A, when gas-liquid two-phase refrigerant is introduced into the throat portion of the nozzle body, it is difficult to stably improve the nozzle efficiency.